<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    
</body>
<script>
    var a = 9;
    var b = 0;
    document.write("hello world")
    document.write("<br>")
    document.write(a/b)
    console.log(typeof(a/b))
    let obj = {name: "John", age: 30, city: "New York"};
    console.log(obj["age"]);
    console.log(obj.name);

    let str = "123";
    let num = 123;
    let boor = true;
    let emitd = null;
    let undef;

    console.log("转字符串：",String(num))
    console.log("转字符串：",num.toString)

    console.log("转数字：",Number(str))
    console.log("转整型：",parseInt(12.34))
    console.log("转浮点型：",parseFloat(num))
</script>
</html>